Password controlled systems are known. In such systems, access to a resource (such as a central computer) is denied unless a predetermined code (password) is initially provided.
In a two-way communication system, subscribers each have an identification (ID) code, which may be analogized to a simple password control mechanism. Whenever a subscriber desires to communicate, a request (which includes the ID code) may be transmitted to a central location. If the subscriber is authorized (i.e., the ID code is recognized by the system) communication is permitted. Unauthorized (unrecognized) subscribers are denied access to the communication resources. For example, operators of Specialized Mobile Radio (SMR) systems provide a communication service to their subscribers in return for a basic monthly rate (which may also include a variable charge depending upon the amount of "air time" used by each subscriber). Each subscriber is billed for each ID code that the system is programmed to recognize. Generally, each subscriber has unlimited access to the SMR system so long as the service bills are paid.
The need for the present invention grew out of the realization by some SMR operators that some of the subscribers are duplicating (or permitting others to duplicate) the memory device that contains the ID code, and installing the duplicated devices in several radios. In this way, the basic monthly fee per unit is avoided since several subscribers now have the "same" ID code. The loss of revenue to the SMR operators is both significant and growing. Although legal recourse may be available, it is both time consuming and costly. Typically, the SMR operator has invested hundreds of thousands of dollars to provide the communication service, and the additional cost and burden of policing the system may be intolerable.
From the above discussion, it will be apparent that conventional password systems are completely unsuited to address this problem. The fundamental problem with simple password systems is that they presuppose that a subscriber desires to maintain the password in secrecy, thereby assisting in the effort to control who has access to the resource. Accordingly, the addition of a separate password (perhaps entered on a keypad of a radio) would be fruitless since this password could be easily disseminated by those who currently duplicate the ID codes. Further, requiring individuals to enter a password prior to requesting a communication channel goes against the custom and practice of the communication industry, and may be overly burdensome to the subscribers. Thus, a need exists to provide a method for allowing easy access to a communication system, while still providing protection to the operators of such communication systems.